The present invention is directed to a method for producing aromatic carbonates and, more specifically, to a method for producing diaryl carbonates through the carbonylation of aromatic hydroxy compounds.
Aromatic carbonates find utility, inter alia, as intermediates in the preparation of polycarbonates. For example, a popular method of polycarbonate preparation is the melt transesterification of aromatic carbonates with bisphenols.
Various methods for preparing aromatic carbonates have been previously described in the literature and/or utilized by industry. A method that has enjoyed substantial popularity in the literature involves the direct carbonylation of aromatic hydroxy compounds with carbon monoxide and oxygen catalyzed by at least one Group 8, 9, or 10 metal source. Further refinements to the carbonylation catalyst composition include the identification of co-catalysts.
The utility of the carbonylation process is strongly dependent on the number of moles of aromatic carbonate produced per mole of Group 8, 9, or 10 metal utilized (i.e. xe2x80x9ccatalyst turnover number or xe2x80x9cTONxe2x80x9dxe2x80x9d). Consequently, much work has been directed to the identification of efficacious process variations that increase catalyst turnover and yield of aromatic carbonate.
As the demand for high performance plastics has continued to grow, still new and improved methods of providing product more economically are needed to supply the market. In this context, various processes and catalyst systems are constantly being evaluated; however, the identities of improved and/or additional effective catalyst systems for these processes continue to elude the industry. Consequently, a long felt, yet unsatisfied need exists for new and improved methods and catalyst systems for producing aromatic carbonates and the like.
The start-up procedure for the carbonylation process is an important step in the overall process. More particularly, an incorrect start-up procedure can result in rapid catalyst inactivation and render a carbonylation catalyst system ineffective for producing high yields of aromatic carbonate. A consistently effective start-up procedure for a carbonylation reaction is a long-felt need in the art.
After diligent experimentation the present inventors have discovered a method for producing aromatic carbonates which comprises an effective start-up procedure. Thus, in one embodiment, the present invention provides a method for producing aromatic carbonates which comprises the steps of:
(i) contacting at a temperature sufficient to keep the mixture molten at least one aromatic hydroxy compound with a catalyst composition comprising the following and any reaction products thereof:
(A) at least one Group 8, 9, or 10 metal or a compound thereof;
(B) at least one salt;
(C) at least one metal co-catalyst; and
(D) optionally, at least one activating solvent;
(ii) optionally heating the mixture at atmospheric pressure to a temperature above that sufficient to keep the mixture molten;
(iii) pressurizing the mixture with carbon monoxide;
(iv) optionally heating the mixture under pressure of carbon monoxide to a temperature above that sufficient to keep the mixture molten;
(v) optionally maintaining the mixture under pressure of carbon monoxide for a time period;
(vi) introducing oxygen to the mixture to a desired concentration of oxygen in carbon monoxide;
(vii) starting gas flow to the mixture at a desired concentration of oxygen and carbon monoxide;
(viii) optionally maintaining gas flow for a time period at less than a desired ultimate temperature for the mixture; and
(ix) optionally heating the mixture to a desired ultimate temperature under flow of gases.
In another embodiment, the invention provides a method for producing aromatic carbonate from a mixture comprising an aromatic hydroxy compound, which comprises the steps of:
(x) maintaining the mixture at a temperature at least sufficient to keep the mixture molten;
(xi) introducing oxygen and carbon monoxide to the mixture to a desired pressure;
(xii) starting gas flow to the mixture at a desired concentration of oxygen and carbon monoxide;
(xiii) heating the mixture to a temperature in a range between that sufficient to keep the mixture molten and a desired ultimate temperature; and
(xiv) contacting the mixture with one or more mixtures comprising aromatic hydroxy compound and one or more catalyst components comprising the following and any reaction products thereof:
(A) at least one Group 8, 9, or 10 metal or a compound thereof;
(B) at least one salt;
(C) at least one metal co-catalyst; and
(D) optionally, at least one activating solvent.
Various other features, aspects, and advantages of the present invention will become more apparent with reference to the following description and appended claims.